The present invention broadly relates to propeller devices and, more specifically, pertains to a new and improved construction of an adjustable propeller or adjustable pitch propeller for marine vessels.
In its more specific aspects the present invention relates to an adjustable pitch propeller for marine vessels having an adjusting or adjustment mechanism for adjusting the pitch angle or pitch of the propeller blades or vanes.
Adjustable propellers of this type are common and serve to adjust the pitch angle of the propeller blades or vanes to different operating conditions of the vessel, such as reversal of direction.
In known propellers the adjusting mechanism acts on the propeller blades in such a manner that the pitch angles of all propeller blades are always equal.
On the other hand it is well known that propellers mounted in the stern of a vessel are subjected to non-uniform or irregular flow conditions, so that each propeller blade encounters differing flow conditions in different angular positions during one revolution. This reduces its efficiency and induces cavitation.
In order to eliminate this disadvantage, it has already been proposed to cyclically vary the pitch angle or pitch of the blades of ship propellers during each revolution, for instance by means of a cam device. This cyclical variation of the pitch angle of each blade is effected during each revolution in relation to the flow conditions that it encounters. In this respect, attention is directed, for instance, to British Pat. No. 325,538, USSR Pat. No. 126,385 or the article "The Pinnate Propeller" in the magazine "Ship and Boat International" of January/February 1978, page 61.
Although in all of these propellers the propeller blades are rotatively adjusted, they are not truly adjustable pitch propellers in the sense described. In truly adjustable pitch propellers a conjoint simultaneous adjustment of all propeller blades to the operating conditions would be possible. In known propellers a continuous modification of the pitch angle of the propeller blades during one revolution is not possible. This would, for instance, be useful for different speeds and different depths of displacement of the hull of the ship. For these reasons such propellers have not been successful in practice.